Page 31 - Materials Science and Engineering An Introduction

1.2 Materials Science and Engineering • 3

properties of materials. In contrast, materials engineering involves, on the basis of these
structure–property correlations, designing or engineering the structure of a material to
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produce a predetermined set of properties. From a functional perspective, the role of a
materials scientist is to develop or synthesize new materials, whereas a materials engi-
neer is called upon to create new products or systems using existing materials and/or to
develop techniques for processing materials. Most graduates in materials programs are
trained to be both materials scientists and materials engineers.
Structure is, at this point, a nebulous term that deserves some explanation. In brief,
the structure of a material usually relates to the arrangement of its internal components.
Subatomic structure involves electrons within the individual atoms and interactions with
their nuclei. On an atomic level, structure encompasses the organization of atoms or
molecules relative to one another. The next larger structural realm, which contains large
groups of atoms that are normally agglomerated together, is termed microscopic, mean-
ing that which is subject to direct observation using some type of microscope. Finally,
structural elements that can be viewed with the naked eye are termed macroscopic.
The notion of property deserves elaboration. While in service use, all materials are
exposed to external stimuli that evoke some type of response. For example, a specimen
subjected to forces experiences deformation, or a polished metal surface reflects light. A
property is a material trait in terms of the kind and magnitude of response to a specific
imposed stimulus. Generally, definitions of properties are made independent of mate-
rial shape and size.
Virtually all important properties of solid materials may be grouped into six differ-
ent categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative. For
each, there is a characteristic type of stimulus capable of provoking different responses.
Mechanical properties relate deformation to an applied load or force; examples include
elastic modulus (stiffness), strength, and toughness. For electrical properties, such as
electrical conductivity and dielectric constant, the stimulus is an electric field. The
thermal behavior of solids can be represented in terms of heat capacity and thermal
conductivity. Magnetic properties demonstrate the response of a material to the ap-
plication of a magnetic field. For optical properties, the stimulus is electromagnetic or
light radiation; index of refraction and reflectivity are representative optical properties.
Finally, deteriorative characteristics relate to the chemical reactivity of materials. The
chapters that follow discuss properties that fall within each of these six classifications.
In addition to structure and properties, two other important components are in-
volved in the science and engineering of materials—namely, processing and perform-
ance. With regard to the relationships of these four components, the structure of a
material depends on how it is processed. Furthermore, a material’s performance is a
function of its properties. Thus, the interrelationship among processing, structure, prop-
erties, and performance is as depicted in the schematic illustration shown in Figure 1.1.
Throughout this text, we draw attention to the relationships among these four compo-
nents in terms of the design, production, and utilization of materials.
We present an example of these processing-structure-properties-performance prin-
ciples in Figure 1.2, a photograph showing three thin disk specimens placed over some
printed matter. It is obvious that the optical properties (i.e., the light transmittance) of each
of the three materials are different; the one on the left is transparent (i.e., virtually all of the

Processing Structure Properties Performance
Figure 1.1 The four components of the discipline of materials science and
engineering and their interrelationship.

2 Throughout this text, we draw attention to the relationships between material properties and structural elements.